For an image, the term monochrome is usually taken to mean the same as black-and-white, but may also be used to refer to other combinations containing only two colors, such as green-and-white, green-and-black. It may also refer to sepia or cyanotype images.

In computing, monochrome has two meanings: it can mean having only one color which is either on or off, or also allowing shades of that color, although the latter is more correctly known as greyscale.

In the physical sense, no real source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration. Even sources such as lasers have some narrow range of wavelengths (known as the linewidth or bandwidth of the source) within which they operate.

In physics, the word is used more generally to refer to electromagnetic radiation of a single wavelength. In the physical sense, no real source of electromagnetic radiation is purely monochromatic, since that would require a wave of infinite duration as a consequence of the Fourier transform's localization property (cf. spectral coherence). Even sources such as lasers have some narrow range of wavelengths (known as the spectral linewidth) within which they operate. In practice, filtered light, diffraction grating separated light and laser light are all routinely referred to as monochromatic. Often light sources can be compared and one be labeled as "more monochromatic" (in a similar usage as monodispersity). And a device which isolates light sources of a narrow bandwidth are called monochromators, even though the bandwidth is often explicitly specified, and thus a collection of wavelengths is understood.

For an image, the term monochrome is usually taken to mean the same as black-and-white or, more likely, grayscale, but may also be used to refer to other combinations containing only two colors, such as green-and-white or green-and-black. It may also refer to sepia or cyanotype images. In computing, monochrome has two meanings:

it may mean having only one color which is either on or off,

allowing shades of that color, although the latter is more correctly known as grayscale.

In film photography, monochrome is the use of black and white film. In digital photography, monochrome is the capture of only shades of black by the sensor.
Originally, all photography was done in monochrome until the invention of color film plates in the early 20th century.